Geochemical comparisons between estuaries with non-industrialised and industrialised catchments: the Huon and Derwent River estuaries, Tasmania
The adjacent Huon and Derwent estuaries in Tasmania have similar climatic and physical characteristics, and provide a good comparison between relatively uncontaminated and industrially polluted estuaries, respectively. Representative samples were collected from both estuaries and analysed for grainsize and trace‐element content (using X‐ray fluorescence and neutron activation analyses). The Huon estuary drains a predominantly forested and agricultural catchment and contains low (baseline) concentrations of trace elements, including lead, zinc and copper. In contrast, the Derwent estuary has a geologically similar yet larger catchment and it passes through an industrialised area in the midestuarine reach. A zinc refinery has, in the past, been a major source of trace‐element contamination. These contaminants are distributed downstream from the refinery by combined fluvial and tidal activity, while the latter also causes upstream movement of contaminants during non‐flood periods. Significant upstream contamination is limited by fluvial bottom flows remobilising contaminated fine sediment during flood periods. Maximum contamination occurs in the region around the refinery with values in the surface sediments ranging from 40 to 565 times baseline levels and from 2 to 55 times the Australian Interim Sediment Quality Guidelines high‐levels for aquatic sediments (maximum 22593 ppm Zn, 3866 ppm Pb and 1182 ppm Cu). In the lower Derwent estuary, contaminant distribution is inversely related to tidal‐flow velocities and is most prominent in the lower energy muddy substrates. Trace‐metal levels in the more recent surficial aquatic sediments are slightly lower than those recorded in a previous study from the area, possibly reflecting the stricter environmental controls now operating.